1. Field of the Invention
This invention relates to adsorbents and more particularly, it relates to a peptized activated carbon/alumina composite and method of preparing the same suitable for us in adsorption processes.
2. Description of the Related Art
The use of activated carbon is considered to be one of the most economical methods for treating water for the removal of a wide range of pollutants. Its heterogeneous pore structure is suitable for removing most waste water pollutants although its capacity for an individual pollutant varies.
Activated carbon is used in drinking water treatment for removing organic pollutants including objectionable taste and odor. Although it is able to adsorb some inorganic molecules, e.g., phosphates and chromates, adsorption sites available for these components are quite limited. Because of lack of capacity for inorganic materials, the adsorber service life is shortened although the overall saturation capacity may not be reached for the organic material.
In gas separation and purification, activated alumina has been used very frequently to remove trace molecules such as carbon dioxide and ammonia, because activated alumina has a high adsorption capacity for these materials at low concentration ranges. However, gas waste streams often contain other pollutants, such as non-polar hydrocarbons, e.g., methane, which activated alumina only weakly adsorbs. This requires an additional step for removal of such organic materials. Thus, it will be understood that there is a great need for an adsorption material which would adsorb both kinds of pollutants.
In the prior art, U.S. Pat. No. 4,499,208 discloses activated carbon pellets suitable for use in the adsorbent beds of pressure swing adsorption systems. The carbon pellets are prepared by mixing a volume-based higher heat capacity, inert inorganic material with a partially activated carbon powder prior to pelletizing of the powder. Dense alumina in the form of corundum is used for this purpose. However, the activated carbon in the form of powder is treated by the addition of a binder, such as pitch, bitumen, tar and tar oil, followed by pelletizing of the powder-binder mixture. The resulting doped adsorbent is designed to enhance the operation of adiabatic pressure swing adsorption processes by decreasing the cyclic temperature change in the adsorbent bed during each processing cycle of the process.
U.S. Pat. No. 1,530,392 discloses a process for making compound adsorbent catalysts wherein the active catalytic components are introduced into a charcoal body which generally serves as a carrier but sometimes is capable of functioning as a catalyst as well as a carrier or adsorbing agent. According to the patent, the active catalytic components are metallic and other elementary substances, including aluminum, zinc, cobalt, copper, etc., and oxides and other compounds of these metals.
U.S. Pat. No. 2,662,860 discloses a method for making a molded alumina carrier for a catalyst which comprises mixing alumina trihydrate with an aluminum salt of a strong acid, e.g., AlCl.sub.3, and water; and extruding the mixture into pellets which are then dried and heated to a temperature above 200.degree. C.
U.S. Pat. No. 3,135,696 discloses a process for the preparation of aluminum oxide and carbon based briquettes for reducing the aluminum oxide with carbon.
U S. Pat. No. 3,158,578 teaches a method for preparing an activated alumina which is useful in bleaching refined cottonseed oil which comprises treating activated alumina with an aqueous solution of sulfurous acid until the alumina is saturated and then drying the treated alumina.
U.S. Pat. No. 3,658,724 discloses an adsorbent oxidation catalyst comprised of an adsorbent which can be a non-combustible refractory of high surface area, such as silica, alumina or activated carbon, mixed with such refractory. However, the adsorbent has an oxidation catalyst incorporated therein or on its outer surfaces.
U.S. Pat. No. 3,842,014 discloses graphite-alumina pellets consisting essentially of a gas or vacuum ground graphite of surface area 50 to 2000 square meters per gram, and, as a binder, alumina of pseudoboehmite structure of crystalline size less than 10 manometers and of surface area 200 to 600 square meters per gram.
U.S. Pat. Nos. 3,941,719 and 3,944,658 (both divisions of Ser. No. 281,434.) describe a method of making a transparent activated nonparticulate alumina by hydrolyzing aluminum alkoxides, treating the hydrolyzed slurry with an acid or a salt to peptize it, heat treating the peptized aqueous slurry above 80.degree. C. until a clear solution is formed, forming a gel either by further heating of the solution or by treating it in an organic base such as urea, and then pyrolyzing the gel at a temperature of 500.degree. to 1200.degree. C. to remove water and residual carbon.
U.S. Pat. No. 4,113,661 discloses a method for making a porous catalyst carrier by treating alpha-alumina monohydrate with a monobasic acid such as nitric acid and then neutralizing the acid with a base such as aqueous ammonia. The resulting material is fed to an extruder, and the extrudate is then dried and calcined.
U.S. Pat. No. 4,140,773 describes a method for making alumina spheres by hydrolyzing aluminum alkoxides and then drying the hydrolyzed alumina to a powder which is then dropped onto a rotating wheel under a peptizing spray, such as nitric acid, acetic acid, formic acid, etc., which is misted onto the wheel, resulting in the formation of spheroidal alumina.
U.S. Pat. No. 4,277,376 describes the formation of a monolithic catalyst support by mixing colloidal gamma alumina, alpha alumina and ceramic fibers with fluidizing and binding agents, water and mineral acid in an amount sufficient to convert the alpha alumina into a gel. The mass is then formed into a body of the desired shape which is dried to substantially remove the added water and then heat treated at 800.degree. to 1000.degree. C.
U.S. Pat. No. 4,705,767 teaches the addition of surface active agents to an acid-peptized alumina. The alumina is peptized with nitric acid, acid nitrates such as aluminum nitrate, acetic acid or formic acid. The acid peptized paste may be subsequently neutralized with ammonium hydroxide. The acid peptized paste is then mixed with a cationic, anionic or nonionic surfactant prior to extrusion.
U.S. Pat. No. 4,058,483 discloses an adsorptive material, useful for removing substances from gases and liquids, in discrete pieces, each comprising an adsorptive carbon and an inorganic adsorptive oxide in a mutual weight proportion between 1:5 and 5:1 and the discrete pieces having been formed by a wet method.
Japanese Pat. No. 60,087,853 discloses a heat resistant adsorbent for hydrocarbon content of exhaust gas which consists of granular activated charcoal, the surface of which is coated with porous alumina. The adsorbent is made from a slurry of boehmite alumina, water and nitric acid to which is added powdered gamma alumina. Thereafter, 2 to 5 mm granular activated charcoal is coated by immersion in the slurry mixture.
The present invention provides an improved adsorbent comprised of activated carbon/alumina formed by peptizing a mixture of alumina and activated carbon.